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I've got a few units like that (Vulcan/Hobart).......is the no ignition light lit? Even if it isn't, you need to check the flame sense rod and or ignitor to verify that they're working properly. If it's a hot surface ignitor, it's possible that it's getting weak even if it looks like it's hot enough to light. If the flame sense rod is eroded, dirty, or warped, you won't be picking up flame consistently enough to keep it lit.

kitchenfixer - The unit is spark ignition with seperate flame sense (rod) built in - I sat and watched the oven for 15minutes or so and watched it stay lit for me. I will look into this further though when i return.

I've worked on several of these units. Is this a digitally controlled unit or old knob style?

From my experience it has been a
1. bad temp probe in the upper right corner of the oven
2. bad thermostat control or thermostat control not calibrated
3. oven doors are not sealing properly or the ball latch is broken.
4. burner assembly is dirty not allowing flame travel to reach its full potential. (Flame only traveling 1/2 way up the burner assembly tube)
5. the orifice is dirty or something is obstructing it.
6. gas pressure low

Remove the bottom panel that has the gas valve shutoff door on it (Should be held on by 6 phillips head screws, 2 on each side and two on the top hidden by the oven doors). Once that is removed you will see the wires for the flame sense, spark ignition wire, gas orifice, and gas line. Remove the metal gas line that has two bolts holding it on (12mm If i recall correctly) then remove the piece of metal that blocks the view of the flame that is held in place with i believe two phillips head screws. put the gas line with orifice back on the burner assembly and then start up the oven. See what the flame does when the oven is heating up

I also had a unit that had a short in one of the wires so when I was called to check it out, it worked fine. Then when I left it started acting up again.

Usually its not due to the ignition or flame sense.

Anytime I have a problem with a specific unit I go to the manufacturers website and download the service manual. Saved my ass plenty of time and the customers time and money. Or you can also call Vulcan hart for support

You can start both ovens up at the same time and observe which oven cycles off first. Having two temp meters makes this fairly simple. If the slower oven doesn't cycle off close to the other I would check manifold pressure, burner condition and orifices.